Various polymers are produced and used in our environment. Polyvinyl chloride, in particular, is applied to various uses similarly to other general-purpose polymers including polyesters and polyolefins, such as polyethylenes and polypropylenes, because polyvinyl chloride is excellent in workability and inexpensive. However, those general-purpose polymers are mass-produced for application not only to the field of basic articles having a long product life cycle but also to the field of commercial articles, such as dairy necessities having a short life of use. Consequently, a large amount of those articles are scrapped, causing environmental pollution. Composite articles formed of resins containing polyvinyl chloride and other polymers are encountered by greater problems.
Various techniques for polymer waste recycling have been studied. There has been growing expectation of using polymer waste as heat source for blast furnaces because of its low cost of waste disposal. However, when polymer waste including those combined or mixed with polyvinyl chloride is incinerated to use the same as a heat source, free chloride liberated from polymer waste damages furnace body refractories. When polyvinyl chloride is burnt, organic chlorine compounds including dioxin and the like highly toxic to human bodies are generated.
Various techniques have been proposed to solve those problems. One of those previously proposed techniques, for example, mixes a solvent capable of dissolving polyvinyl chloride in a mixture of various polymers, filters out insoluble solid matters, and injects steam into the solvent to solidify and precipitate polyvinyl chloride dissolved in the solvent. However, this method makes the solvent evaporate so that polyvinyl chloride is solidified after the polyvinyl chloride concentration has exceeded the solubility of polyvinyl chloride in the solvent. Thus the method is unsuitable for a continuous operation that evaporates a large amount of solvent continuously, and there is room for improvement.
The present invention has been made in view of the foregoing circumstances and it is therefore an object of the present invention to provide a method of recovering polyvinyl chloride from waste including polyvinyl chloride by a continuous operation, and an system for carrying out the method.